TWI893249B - Fe-based alloy powder - Google Patents

Abstract

The object of the present invention is to provide a hot working tool steel powder suitable for laminated molding, wherein the laminated molded body made from the powder has both high thermal conductivity and hardness. The present invention provides an Fe-based alloy powder containing, by mass%, 0.40 < C < 0.70, Si < 0.60, Mn < 0.90, Cr < 4.00, Ni < 2.00, 0.90 < Mo < 1.20, W < 2.00, V < 0.60, and Al < 0.10, with the remainder being Fe and unavoidable impurities, satisfying equations (1) and (2), K1 > 21.7 ... equation (1); K2 > 29.0 ... equation (2), and having an average particle size D ₅₀ of 200 μm or less.

Description

Fe-based alloy powder

The present invention relates to an Fe-based alloy powder suitable for use as hot work tool steel powder. In particular, the present invention relates to an Fe-based alloy powder suitable for processes for forming molded bodies using methods such as three-dimensional lamination, melt spraying, laser coating, overlay welding, and hot isotropic pressing.

In recent years, additive manufacturing has become increasingly popular for the production of metal structures. Representative methods for metal additive manufacturing include the powder bed method (powder bed fusion bonding method) and the metal deposition method (directed energy deposition method).

In the powder bed method, laser or electron beam irradiation melts and solidifies the irradiated areas of the powder bed. This melting and solidification causes the powder particles to bond together. Irradiation is selectively applied to a portion of the metal powder, leaving the unirradiated areas unmelted. Only the irradiated areas form a bonding layer.

New metal powder is then applied to the resulting bonding layer and irradiated with a laser beam or electron beam. This irradiation causes the metal particles to melt and solidify, forming a new bonding layer. Furthermore, the new bonding layer bonds with the existing bonding layer.

By repeating the melting and solidification steps through irradiation, the aggregate of the bonded layers gradually grows. This growth results in a three-dimensional object. Using this layer-by-layer method, complex shapes can be easily obtained.

As a powder bed method, a layered molding method discloses the following procedure for manufacturing a three-dimensional shaped body: a mixture of iron-based powder and one or more powders selected from the group consisting of nickel, nickel-based alloys, copper, copper-based alloys, and graphite is used as metal powder for metallographic molding, and a powder layer forming step of laying down the metal powder, a sintering layer forming step of irradiating the powder layer with a beam to form a sintered layer, and a step of removing the surface of the body by cutting are repeated to form a sintered layer to manufacture a three-dimensional shaped body (see Patent Document 1).

Metal layering has also attracted attention as a technology for forming molds. Specifically, attempts have been made to use martensitic steels and SKD61 as powder materials. However, these steels have a low thermal conductivity of approximately 20 W/m/K, resulting in poor cooling efficiency when used in hot stamping molds. Consequently, cooling the mold during use takes time, reducing the cycle speed required for continuous production.

Regarding molds formed using conventional forging methods such as forging and stretching, a mold steel with high hardness and high heat conductivity suitable for die casting and hot stamping has been proposed (see Patent Document 2). However, the proposed mold steel is not intended to be manufactured using the metal layer forming method, but rather is intended to be manufactured using conventional forging methods. Because the proposed metal mold steel is forged using conventional methods, it has the problem of coarse carbides that easily form, acting as starting points for fatigue failure, and is therefore not considered sufficient for use in the metal layer forming method.

Furthermore, a powder with the following composition has been proposed as a mold steel suitable for metal lamination: 0.15 < C < 0.34, 0.0 < Si < 0.52, 4.00 < Cr < 5.72, -0.05814 × [Cr] + 0.4326 < Mn < -0.2907 × [Cr] + 2.4628, 0.72 < Mo < 1.60, 0.20 < V < 0.61, with the remainder being Fe and unavoidable impurities (see Patent Document 3). However, the thermal conductivity of this proposed mold steel remains between 25.2 and 34.7 W/m/K, failing to provide the market-required high thermal conductivity exceeding 35.0 W/m/K and strength required for mold steel suitable for lamination. [Prior Art Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Application Publication No. 2008-81840 [Patent Document 2] Japanese Patent Application Publication No. 2018-119177 [Patent Document 3] Japanese Patent Application Publication No. 2015-224363

[The problem that the invention aims to solve]

Traditionally, martensitic steels such as SKD61, which are suitable for the laminated forming process, have low thermal conductivity. Therefore, when these steels are used in molds requiring cooling mechanisms, such as die casting and hot stamping, the mold takes time to cool, slowing production cycles. Consequently, there is a demand for mold steels with high thermal conductivity that can improve cooling efficiency.

Furthermore, mold steels require high hardness. To increase hardness, various alloying elements are added. These alloying elements dissolve in the matrix. Solvent-bound alloying elements increase the scattering frequency of conductive electrons within the matrix, generally reducing thermal conductivity. Therefore, to improve thermal conductivity, it is necessary to minimize the amount of alloying elements, while also ensuring the hardness required for mold steel.

One of the issues to be addressed by the present invention is to provide a hot working tool steel powder suitable for layered molding. The layered molded bodies produced using this powder can have both high thermal conductivity and hardness (both hardness after quenching and tempering and hardness after softening at high temperatures).

Another problem to be solved by the present invention is to provide a hot working tool steel powder suitable for use in manufacturing hot working tools such as molds using a molding method such as a powder bed layer-building method, and having adequate fluidity to allow the powder to be evenly applied. [Means for Solving the Problem]

As a result of extensive research, the inventors have discovered that by using Fe-based alloy powders with a composition that satisfies the defined ranges and equations 1 and 2 and a specific size to produce a molded body, a molded body can be obtained that has both high thermal conductivity and hardness (hardness after quenching and tempering, and hardness after being held at high temperatures and softened) and is suitable for use in hot working tools such as molds.

The present invention relates to an Fe-based alloy powder comprising, by mass%, 0.40 < C < 0.70, Si < 0.60, Mn < 0.90, Cr < 4.00, Ni < 2.00, 0.90 < Mo < 1.20, W < 2.00, V < 0.60, and Al < 0.10, with the remainder being Fe and unavoidable impurities. The amounts of C, Si, Mn, Cr, Ni, Mo, W, V, and Al contained in the aforementioned Fe-based alloy powder are set to [C] (mass %), [Si] (mass %), [Mn] (mass %), [Cr] (mass %), [Ni] (mass %), [Mo] (mass %), [W] (mass %), [V] (mass %), and [Al] (mass %), respectively, and K1 is set to 9.2 [C] + 3.7 [Si] + 18.1 [Mo] + 0.8 [W]; K2 = 70.2 - 22.1 [C] - 1.6 [Si] - 5.4 [Mn] - 5.8 [Cr] - 5.2 [Ni] - 5.3 [Mo] - 1.0 [W] - 2.5 [V] - 0.3 [Al], satisfying equations (1) and (2), K1 > 21.7 ... equation (1); K2＞29.0 ...Formula (2), and the average particle size _D50 is 200 μm or less. [Effects of the Invention]

The present invention provides an Fe-based alloy powder suitable for use as a raw material powder in the production of hot working tools such as molds using methods such as powder bed layer-building methods. The Fe-based alloy powder of the present invention exhibits moderate fluidity, and molded bodies produced from this powder can achieve a thermal conductivity of 34.0 W/m/K or higher, a quenched and tempered hardness of 48.0 HRC or higher, and a hardness of 33.0 HRC or higher after being held at 600°C for 100 hours. Therefore, the Fe-based alloy powder of the present invention is suitable for producing hot working tools such as molds that exhibit both high thermal conductivity and high hardness using layer-building methods.

[Preferred Embodiment of the Invention] ≪Fe-Based Alloy Powder≫

Before explaining how to produce a molded object using the Fe-based alloy powder of the present invention, the reasons for defining the composition range of the Fe-based alloy powder of the present invention will be explained.

The Fe-based alloy powder of the present invention is an Fe-based alloy powder containing, by mass%, 0.40<C<0.70, Si<0.60, Mn<0.90, Cr<4.00, Ni<2.00, 0.90<Mo<1.20, W<2.00, V<0.60, and Al<0.10, with the remainder being Fe and unavoidable impurities. The amounts of C, Si, Mn, Cr, Ni, Mo, W, V, and Al contained in the Fe-based alloy powder are set to [C] (mass %), [Si] (mass %), [Mn] (mass %), [Cr] (mass %), [Ni] (mass %), [Mo] (mass %), [W] (mass %), [V] (mass %), and [Al] (mass %), respectively, and K1 is set to 9.2[C]+3.7[Si]+18.1[Mo]+0.8[W]; K2=70.2-22.1[C]-1.6[Si]-5.4[Mn]-5.8[Cr]-5.2[Ni]-5.3[Mo]- 1.0[W]-2.5[V]-0.3[Al], satisfying equations (1) and (2), K1＞21.7 …Equation (1); K2＞29.0 ...Formula (2), and the average particle size _D50 is 200 μm or less. Furthermore, the percentages of the chemical compositions below are mass %.

C: More than 0.40% but less than 0.70% C is an element that strengthens the matrix through solid solution, forming carbides and promoting precipitation. In mold steels made using conventional forging methods, increasing the carbon content promotes microsegregation. However, because laminated steel forms fine carbides through rapid cooling, it can contain more carbon than forged materials to increase hardness. A C content exceeding 0.40% achieves sufficient quenching and tempering hardness. On the other hand, a C content exceeding 0.70% promotes microsegregation, reducing toughness. Furthermore, increasing the amount of dissolved C reduces the thermal conductivity of the steel. Therefore, the C content is set to more than 0.40% but less than 0.70%. A C content of 0.45% or more is preferred. For example, the C content can be 0.50% or greater. It is preferably 0.65% or less, and even more preferably 0.60% or less. The above lower limits may be combined with any of the above upper limits. In a preferred embodiment, the C content is greater than 0.40% and less than 0.60%.

Si: Less than 0.60% Si is an element that increases hardness by forming a solid solution in the matrix. It also has the effect of improving softening resistance. However, when Si exceeds 0.60%, it dissolves into the matrix without forming carbides, significantly reducing thermal conductivity. Therefore, Si is set to less than 0.60%. Si is preferably 0.55% or less, more preferably 0.40% or less, and even more preferably 0.30% or less. The lower limit of Si can be 0% or more. Si is preferably 0.03% or more. For example, Si can be 0.05%, 0.10%, or 0.15%. The above lower limits may be combined with any of the above upper limits.

Mn: Less than 0.90% Mn is an element that improves hardenability and suppresses the loss of toughness caused by the formation of molten iron. It also has the effect of improving softening resistance. However, when Mn exceeds 0.90%, it dissolves in the matrix and reduces thermal conductivity. Therefore, the Mn content is set to less than 0.90%. It is preferably less than 0.80%. Mn can be, for example, 0.75% or less, 0.70% or less, 0.65% or less, or 0.60% or less. The lower limit of Mn can be 0% or more. It is preferably 0.10% or more. It can be, for example, 0.15% or more, 0.20% or more, 0.25% or more, or 0.30% or more. The above lower limits may be combined with any of the above upper limits.

Cr: Less than 4.00% Cr is an element that improves hardenability and suppresses the loss of toughness caused by the formation of molten iron. It also has the effect of improving softening resistance. However, when Cr exceeds 4.00%, it dissolves in the matrix and reduces thermal conductivity. Therefore, the Cr content is set to less than 4.00%. The Cr content is preferably 3.50% or less, more preferably 3.00% or less, and even more preferably 2.00% or less. From the perspective of improving oxidation resistance, the lower limit of Cr is preferably greater than 0%. The Cr content is preferably 0.04% or more, more preferably 0.10% or more, more preferably 0.20% or more, more preferably 0.30% or more, more preferably 0.40% or more, and even more preferably 0.50% or more. The above lower limits may be combined with any of the above upper limits.

Ni: Less than 2.00% Nitride improves hardenability and suppresses the loss of toughness caused by the formation of molten iron. However, Ni dissolves in the matrix without forming carbides, which reduces thermal conductivity. When Ni exceeds 2.00%, thermal conductivity decreases significantly. Therefore, the Ni content is set to less than 2.00%. Ni is preferably 1.96% or less, more preferably 1.90% or less, more preferably 1.80% or less, more preferably 1.70% or less, more preferably 1.60% or less, and even more preferably 1.50% or less. The lower limit of Ni may be 0% or more. Ni is preferably 0.02% or more. The Ni content can be, for example, 0.10% or more, 0.20% or more, 0.30% or more, 0.40% or more, or 0.50% or more. The above lower limits may be combined with any of the above upper limits.

Mo: Exceeding 0.90% and less than 1.20% Mo is an element that promotes secondary hardening during tempering and increases quenching and tempering hardness. The addition of Mo reduces thermal conductivity minimally but significantly increases hardness. Therefore, Mo is set to over 0.90%. However, exceeding 1.20% increases the amount of Mo remaining in the matrix, reducing thermal conductivity. Therefore, Mo is set to over 0.90% and less than 1.20%. Mo is preferably between 0.93% and 1.18%.

W: Less than 2.00% W is an element that promotes secondary hardening during tempering and increases quenched and tempered hardness. However, when W exceeds 2.00%, the amount of W remaining in the matrix increases, reducing thermal conductivity. Therefore, W is set to less than 2.00%. W is preferably 1.97% or less. Examples include 1.90% or less, 1.80% or less, 1.70% or less, 1.60% or less, or 1.50% or less. The lower limit of W may be 0% or more. W is preferably 0.02% or more. Examples include 0.10% or more, 0.20% or more, 0.30% or more, 0.40% or more, or 0.50% or more. The above lower limits may be combined with any of the above upper limits.

V: Less than 0.60% V is an element that promotes secondary hardening during tempering and increases quenching and tempering hardness. However, when V exceeds 0.60%, the amount of V remaining in the matrix increases, reducing thermal conductivity. Therefore, V is set to less than 0.60%. V is preferably 0.57% or less, more preferably 0.50% or less, and even more preferably 0.45% or less. The lower limit of V may be 0% or more. V is preferably 0.01% or more, more preferably 0.10% or more, more preferably 0.20% or more, and even more preferably 0.25% or more. The above lower limits may be combined with any of the above upper limits. In a preferred embodiment, V is 0.25% or more and 0.45% or less.

Al: Less than 0.10% Al is an element that forms nitrides and suppresses grain coarsening during quenching. However, adding more than 0.10% Al results in excessive Al nitride formation, which reduces toughness. Therefore, the Al content is set to less than 0.10%. Al is preferably 0.09% or less. For example, Al can be 0.08% or less or 0.07% or less. The lower limit of Al can be 0% or more. Al is preferably 0.01% or more. For example, Al can be 0.02% or more or 0.03% or more. The above lower limits may be combined with any of the above upper limits.

Formula (1): K1 > 21.7 When the amounts of C, Si, Mo, and W contained in the Fe-based alloy powder of the present invention are set to [C] (mass %), [Si] (mass %), [Mo] (mass %), and [W] (mass %), respectively, K1 is defined as follows. K1 = 9.2 [C] + 3.7 [Si] + 18.1 [Mo] + 0.8 [W]

The value of K1 is an indicator of quenching and tempering hardness. The larger the value of K1, the greater the quenching and tempering hardness. Here, the value of K1 is set to be greater than 21.7. In order to increase the value of K1, the addition of elements such as C, Si, Mo, and W is effective, especially the addition of C and Mo is effective. By setting the composition with a K1 value greater than 21.7, the quenching and tempering hardness of the molded body made from the powder of the present invention will be able to have the so-called excellent hardness of 48.0HRC or more. The value of K1 may be, for example, greater than 22.0, greater than 23.0, greater than 24.0, or greater than 25.0. The upper limit value of K1 may be, for example, 35.0, 33.0, or 30.0. The above-mentioned upper limit values may be combined with any of the above-mentioned lower limit values.

Formula (2): K2>29.0 When the amounts of C, Si, Mn, Cr, Ni, Mo, W, V, and Al contained in the Fe-based alloy powder of the present invention are set to [C] (mass %), [Si] (mass %), [Mn] (mass %), [Cr] (mass %), [Ni] (mass %), [Mo] (mass %), [W] (mass %), [V] (mass %), and [Al] (mass %), respectively, K2 is defined as follows. K2=70.2-22.1[C]-1.6[Si]-5.4[Mn]-5.8[Cr]-5.2[Ni]-5.3[Mo]-1.0[W]-2.5[V]-0.3[Al]

The K2 value is an indicator of thermal conductivity. When the K2 value is below 29.0, the amount of alloying elements remaining in the matrix increases, resulting in a decrease in thermal conductivity. Therefore, the K2 value is set to be greater than 29.0. Examples of K2 values include 30.0, 31.0, 32.0, or 33.0. The upper limit of K2 can be, for example, 50.0. These upper limits can be combined with any of the lower limits.

Average Particle Size _D50 : 200 μm or less. Powder bed layering requires excellent flowability to ensure smooth and orderly deposition of the powder. To facilitate fabrication, the average particle size _D50 of the powder of the present invention is set to 200 μm or less. The average particle size _D50 is preferably 10 μm to 100 μm, more preferably 20 μm to 60 μm, and even more preferably 25 μm to 45 μm.

The average particle size _D50 is the particle size at the point where the cumulative volume of the powder is 50%, calculated from the cumulative number distribution curve based on the total volume of the powder, with the total volume of the powder as 100%. The average particle size _D50 is measured using laser diffraction scattering. A suitable device for this measurement is the Nikkiso Co., Ltd.'s Microtrac MT3000 laser diffraction/scattering particle size distribution measurement device. Powder and pure water are passed through the device's cell, and the particle size is measured based on the light scattering data from the particles.

Molded Articles The molded articles of the present invention are produced from the Fe-based alloy powder of the present invention. The molding powder material used to produce the molded articles of the present invention may consist solely of the Fe-based alloy powder of the present invention or may include materials other than the Fe-based alloy powder of the present invention. The molding powder material may include, for example, a powder binder (e.g., resin powder).

The molded article of the present invention comprises an Fe-based alloy having substantially the same composition as the Fe-based alloy powder of the present invention, namely, an Fe-based alloy containing, by mass%, 0.40＜C＜0.70, Si＜0.60, Mn＜0.90, Cr＜4.00, Ni＜2.00, 0.90＜Mo＜1.20, W＜2.00, V＜0.60, Al＜0.10, the remainder being composed of Fe and unavoidable impurities. When the amounts of C, Si, Mn, Cr, Ni, Mo, W, V, and Al contained in the Fe-based alloy are set to [C] (mass %), [Si] (mass %), [Mn] (mass %), [Cr] (mass %), [Ni] (mass %), [Mo] (mass %), [W] (mass %), [V] (mass %), and [Al] (mass %), and set to K1 = 9.2 [C] + 3.7 [Si] + 18.1 [Mo] + 0.8 [W]; K2 = 70.2 - 22.1 [C] - 1.6 [Si] - 5.4 [Mn] - 5.8 [Cr] - 5.2 [Ni] - 5.3 [Mo] - 1.0 [W] - 2.5 [V] - 0.3 [Al], equations (1) and (2) are satisfied, K1 > 21.7 ...Formula (1); K2＞29.0   ...Formula (2). The molded body is preferably composed of the above-mentioned Fe-based alloy. The composition of the above-mentioned Fe-based alloy is substantially the same as the composition of the Fe-based alloy powder of the present invention. Therefore, the above description regarding the amounts of C, Si, Mn, Cr, Ni, Mo, W, V, and Al contained in the Fe-based alloy powder of the present invention, as well as the above description regarding Formulas 1 and 2, can also be applied to the above-mentioned Fe-based alloy.

In one embodiment, the method for producing a molded body of the present invention comprises: (1) preparing the Fe-based alloy powder of the present invention, and (2) melting and solidifying the Fe-based alloy powder prepared in step (1) to obtain a molded body.

The steps of melting and solidifying the Fe-based alloy powder preferably involve a process that rapidly melts and then rapidly solidifies the Fe-based alloy powder. Examples of molding methods that include this process include three-dimensional (3D) molding, melt spraying, laser coating, and overlay welding. Among these, three-dimensional (3D) molding is preferred. Three-dimensional (3D) molding can be performed, for example, using a 3D printer. A powder bed molding method is preferred. The following describes a powder bed molding method.

The powder bed layering method uses a 3D printer to irradiate a layer of Fe-based alloy powder with a laser beam or electron beam. This irradiation rapidly heats and melts the particles. The particles then rapidly solidify. This melting and solidification process bonds the particles together. Irradiation is performed selectively on a portion of the Fe-based alloy powder. Unirradiated areas of the Fe-based alloy powder remain unmelted, forming a bonding layer only in the irradiated areas.

The bonding layer is then covered with Fe-based alloy powder. This Fe-based alloy powder is then irradiated with a laser beam or electron beam. The irradiation causes the particles to rapidly melt and then rapidly solidify. This melting and solidification causes the particles within the Fe-based alloy powder to bond with one another, forming a new bonding layer. This new bonding layer also bonds with the existing bonding layer.

By repeating the process of "laying Fe-based alloy powder to a thickness of tens of microns and bonding it through irradiation," the aggregate of the bonding layer gradually grows. This growth results in a desired three-dimensional object. Using the layer-by-layer method, complex shapes can be easily obtained.

Thermal conductivity of quenched and tempered molded parts: 34.0 W/m/K or higher The thermal conductivity of quenched and tempered molded parts is significantly correlated with cooling efficiency when used in hot working tools such as hot stamping or die casting molds. Therefore, this value is related to the production cycle speed. To improve cooling efficiency, the thermal conductivity of quenched and tempered molded parts at room temperature is preferably 34.0 W/m/K or higher, and more preferably 40.0 W/m/K or higher. "Room temperature" refers to 25±5°C (preferably 25°C).

Hardness of the shaped part after quenching and tempering (quenching and tempering hardness): 48.0 HRC or higher The hardness of the shaped part after quenching and tempering is essential for ensuring sufficient life when used in hot working tools such as dies for hot stamping or die casting. The hardness of the shaped part after quenching and tempering is preferably 48.0 HRC or higher, and more preferably 50.0 HRC or higher.

Hardness of the molded part after holding at 600°C for 100 hours: 33.0 HRC or higher Evaluating the hardness of the molded part after holding at 600°C for 100 hours is crucial for extending the life of hot working tools such as dies for hot stamping or die casting. Ensuring resistance to softening, maintaining hardness at high temperatures, allows the molded part to maintain its hardness even after prolonged use as a hot working tool such as a die. Therefore, the hardness of the molded part after holding at 600°C for 100 hours is preferably 33.0 HRC or higher. The hardness of the molded part after holding at 600°C for 100 hours is measured after holding the molded part at 600°C for 100 hours after quenching and tempering. [Example]

(Examples 1-25 and Comparative Examples 1-13) In Examples 1-25 and Comparative Examples 1-13, raw materials having the chemical compositions listed in Tables 1A and 1B were produced into Fe-based alloy powders by gas atomization. Specifically, the raw materials were heated by high-frequency induction heating in a vacuum within an aluminum crucible to form a molten alloy. The molten alloy was then dropped from a 5 mm diameter nozzle located at the bottom of the crucible. High-pressure argon gas was then injected into the melt, causing the molten metal to be finely divided and rapidly cooled, resulting in a large amount of fine powder. The resulting powder was classified to a particle size of 63 μm or less, yielding the Fe-based alloy powders of Examples 1-25 and Comparative Examples 1-12. The average particle size D ₅₀ (μm) of the Fe-based alloy powders of Examples 1-25 and Comparative Examples 1-12 is shown in Tables 1A and 1B. As described above, the average particle size D ₅₀ was measured by laser diffraction scattering.

[Molding] The Fe-based alloy powders of Examples 1-25 and Comparative Examples 1-12 were each molded using a three-dimensional multilayer molding apparatus (manufactured by EOS, trade name "EOS-M280") to produce a 10 mm × 10 mm × 10 mm rectangular parallelepiped.

[Heat Treatment] The resulting molded body was subjected to the following heat treatments (quenching and tempering). Quenching: Hold at 1030°C for 30 minutes, then oil cool. Tempering: Hold at 600°C for 60 minutes, then repeat air cooling twice.

[Thermal Conductivity Measurement] Thermal conductivity was measured using the laser flash method. After quenching and tempering, the molded product was trimmed into a circular plate with a diameter of 10 mm and a thickness of 1 mm for testing. The thermal conductivity at room temperature is shown in Tables 2A and 2B.

[Hardness Measurement] Quenching and tempering hardness was measured using a Rockwell hardness tester, measuring the hardness of a surface perpendicular to the lamination direction of the shaped body after quenching and tempering. The results are shown in Tables 2A and 2B.

[Hardness Measurement after High-Temperature Holding] After quenching and tempering, the molded parts were held at 600°C for 100 hours and then measured for hardness using the same method as above. The results are shown in Tables 2A and 2B.

As shown in Table 1A, the Fe-based alloy powders of Examples 1-25 satisfy the compositions defined in the present invention and Equations 1 and 2. As shown in Table 2A, the molded bodies produced from the Fe-based alloy powders of Examples 1-25 exhibit thermal conductivity of 34.0 W/m/K or higher, demonstrating excellent cooling efficiency. Furthermore, the molded bodies exhibit excellent hardness, with hardnesses of 48.0 HRC or higher after quenching and tempering, and 33.0 HRC or higher after high-temperature holding.

On the other hand, as shown in Tables 1B and 2B, the molded bodies made from the powders of the comparative examples have poor thermal conductivity or hardness. For example, the amount of C in Comparative Example 1 is small, and K1 in Formula (1) is also low, so the hardness after quenching and tempering is poor, and the hardness after high temperature holding is also poor. The amount of C in Comparative Example 2 is too much, and the inherent C amount increases, which reduces the thermal conductivity of the steel, and the hardness after high temperature holding is also poor. The amount of Si in Comparative Example 3 is too much, so the thermal conductivity is reduced. The value of K1 in Formula (1) in Comparative Example 4 is low, so the hardness after quenching and tempering is poor, and the hardness after high temperature holding is also poor. The amount of Cr in Comparative Example 5 is too much, and the value of K2 in Formula (2) is also low, so the thermal conductivity is reduced. In Comparative Example 6, the amount of Ni is excessive, and the value of K2 in Formula (2) is low, so the thermal conductivity is reduced, and the hardness after high-temperature holding is also poor. In Comparative Example 7, the amount of Mo is insufficient, and the value of K1 in Formula (1) is low, so the hardness after quenching and tempering is poor, and the hardness after high-temperature holding is also poor. In Comparative Example 8, the amount of Mo is excessive, and the influence of Mo remaining in the matrix causes the thermal conductivity to be reduced, and the hardness after high-temperature holding is also poor. In Comparative Example 9, the amount of W is excessive, and the influence of W remaining in the matrix causes the thermal conductivity to be reduced, and the hardness after high-temperature holding is also poor. In Comparative Example 10, the amount of V is excessive, and the influence of V remaining in the matrix causes the thermal conductivity to be reduced, and the hardness after high-temperature holding is also poor. The K2 value of formula (2) in Comparative Example 11 is low, so the thermal conductivity is reduced, and the hardness after high-temperature holding is also poor. The K1 value of formula (1) in Comparative Example 12 is low, so the quenching and tempering hardness is reduced, and the hardness after high-temperature holding is also poor. The K2 value of formula (2) in Comparative Example 13 is low, so the quenching and tempering hardness and the hardness after high-temperature holding are poor. [Industrial Applicability]

The Fe-based alloy powder of the present invention is suitable for manufacturing hot working tools such as dies for hot stamping or die casting by using layered molding.

Claims (1)

An Fe-based alloy powder comprises, in mass %, 0.40<C<0.70, 0<Si<0.60, 0<Mn<0.90, 0<Cr<4.00, 0<Ni<2.00, 0.90<Mo<1.20, 0<W<2.00, 0<V<0.60, 0<Al<0.10, with the remainder being Fe and unavoidable impurities. The amounts of C, Si, Mn, Cr, Ni, Mo, W, V, and Al contained in the Fe-based alloy powder are set to [C] (mass %), [Si] (mass %), [Mn] (mass %), [Cr] (mass %), [V ... ), [Ni] (mass %), [Mo] (mass %), [W] (mass %), [V] (mass %) and [Al] (mass %), and setting K1 = 9.2 [C] + 3.7 [Si] + 18.1 [Mo] + 0.8 [W]; K2 = 70.2-22.1 [C] - 1.6 [Si] - 5.4 [Mn] - 5.8 [Cr] - 5.2 [Ni] - 5.3 [Mo] - 1.0 [W] - 2.5 [V] - 0.3 [Al], satisfying equations (1) and (2), K1> 21.7 ... equation (1); K2> 29.0 ... equation (2), and the average particle size D ₅₀ is less than 200 μm.